타입케스팅 체크

var m:Sprite=new Sprite;
var mNew:DisplayObject =m;

if(mNew is Sprite){

var mk:Sprite = Sprite(mNew); //런타임에 에러가뜸

var mk:Spirte = mNew as Sprite; //런타임 에러가 안뜸
//타입케스팅

}